Preheat oven to 350°F (175°C).
Mix graham cracker crumbs, sugar, and melted butter.
Press mixture firmly into a 9-inch pie dish.
Bake crust for 8–10 minutes and allow it to cool slightly.
In a bowl, whisk sweetened condensed milk, key lime juice, lime zest, and egg yolks until smooth.
Pour filling into the pre-baked crust.
Bake for 12–15 minutes until the center is just set.
Cool at room temperature, then refrigerate for at least 3 hours.
Whip heavy cream with powdered sugar until soft peaks form.
Spread or pipe whipped cream over chilled pie.
Garnish with lime slices before serving.
